1. Field of the Invention
The present invention relates to a technique for measuring a three-dimensional shape of the surface of an object by projecting a projection pattern onto an object and capturing an image of the projected projection pattern.
2. Description of the Related Art
The conventional active three-dimensional shape measurement projects a fringe pattern onto an object, captures an image of the projected fringe pattern, and calculates distortions of the fringe pattern based on the captured image, thus measuring a three-dimensional shape and surface distortion conditions of the object. In particular, the phase shift method has been widely applied. This method projects a fringe pattern having a sinusoidal-wave-shaped luminance variation onto an object, and captures a plurality of images while shifting the phase of the fringe pattern, thus measuring a three-dimensional shape and surface distortion conditions of the object with high density and high accuracy.
However, the phase shift method premises that a plurality of images is captured in a state where the shape of the object remains unchanged, and phase calculation is performed. Therefore, the phase shift method has a problem that measurement cannot be accurately performed if the object moves or transforms during image capturing.
To solve this problem, there has been employed a technique for performing phase calculation by capturing only one image, instead of a plurality of images. A method discussed in Ryusuke Sagawa, Hiroshi Kawasaki, Ryo Furukawa, Shota Kiyota, “Dense One-shot 3D Reconstruction by Detecting Continuous Regions with Parallel Line Projection”, Collected Papers of Meeting on Image Recognition and Understanding (MIRU2011), pp. 416-423 (2011) projects one piece of vertical and horizontal line patterns uniformly colored in green and blue in a specific order onto an object, and captures only one image of the projected line patterns. More specifically, the method corresponds the order of the projected line patterns with the order of the captured line patterns, applies a Gabor filter to the captured line patterns as a fringe pattern having a luminance variation, and performs phase calculation based on the one captured image, thus measuring a three-dimensional shape with high density.
However, in the method discussed in the above-described nonpatent document, since two different colors are used for the line patterns in the projection pattern, the waveforms of the line patterns of respective colors are largely affected by the surface color of the object, resulting in failed correspondence between the order of the projected line patterns and the order of the captured line patterns. Further, the measurement accuracy is remarkably degraded because phase calculation cannot be accurately performed.